This project seeks to improve our understanding of the detailed circuitry of the thalamus and its relation to arousal, sleep-wakefulness cycles, and information transfer from subcortical relays to the cerebral cortex. The specific aim of this project is to identify the details of the relation of potential neuromodulatory axonal arborizations with the neurons and their dendrites in the thalamic reticular nucleus (TRN) and in the intralaminar nuclei (ILN) of the thalamus. The goal is to further our understanding of the neural circuitry underlying thalamic gating functions. Using anterograde transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), the thalamic distributions of axons arising in the mesencephalic reticular formation (MRF) were examined and compared with the thalamic projections arising in the pontine reticular formation (PRF). Some marked distinctions in the thalamic projections arising at these two levels of the reticular formation were found, distinctions which may underlie the striking differences in forebrain activation levels known to result following brainstem is transsections at these two levels. The study of topography in the external pallidal (GPe) projection upon the TRN was completed during this past year. The general rostrocaudal topography in the GPe projection upon the TRN was detailed with retrograde tracing methods as well as with anterograde tracing methods. In addition, the cells of origin of a projection from the contralateral cortex upon the thalamic intralaminar nuclei (ILN) was mapped using retrogradely transported fluorescent dyes. The contralateral inputs upon the ILN were found to arise from neurons deep in layer VI of the frontal lobe.